Differential Effects of the Substituted Pyridazinone Herbicide Sandoz 9785 on Lipid Composition and Biosynthesis in Photosynthetic and Non-Photosynthetic Marine Microalgae

Abstract

The effect of the substituted pyridazinone, 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone (Sandoz 9785), on fatty acid synthesis in two photosynthetic species (Chroomonas salina and Nannochloropsis oculata) and one non-photosynthetic species (Crypthecodiniun cohnii) of marine microalgae were examined. Effects were more obvious in C. salina than in C. cohnii or N. oculata. In C. cohnii the relative distribution amongst polyunsaturated fatty acids (PUFA) of radioactivity incorporated from 14C-acetate was not influenced by the herbicide to any great extent and no major changes in the fatty acid composition of lipid fractions were observed. In C. salina, Sandoz 9785 reduced the proportions of radioactivity recovered in 20: 5 (n−3) and 22: 6 (n−3) of the phospholipid fraction. The distribution pattern of radioactivity in the fatty acids of monogalactosyldiacylglycerol (MGDG) in this species was not greatly affected by the herbicide whereas its presence significantly reduced the proportions recovered in 18: 4 and 20: 1 in digalactosyldiacylglycerol (DGDG). The level of 20: 5 (n−3) in DGDG of C. salina was increased from 4.0 to 19.8% by growing the algae in the presence of Sandoz 9785. The only notable effect of the herbicide on the synthesis of PUFA in N. oculata was a reduction from 18.3% to 11.3% of the proportion of radioactivity recovered in 20: 5 in phospholipids. The herbicide had no effect on the distribution of radioactivity in PUFA of galactolipids or on the fatty acid composition of lipid fractions. The results are discussed in relation to the potential role of galactolipids and phospholipids as substrates for desaturations involved in the formation of long chain PUFA in marine microalgae.